1. Field of the Invention
The present invention relates to a driving circuit for a vibration wave motor.
2. Related Background Art
For efficient driving of a vibration wave motor the use of resonance frequency is desirable, and, for achieving this objective the present applicant already proposed, in the Japanese Patent Application No. 226566/1985, to detect the vibration state of the motor with a monitor electrode, and to maintain a constant phase difference between the signal from the monitor electrode and the driving signal.
Such a method allows the vibration wave motor to be driven always at its resonance frequency, but is inconvenient for speed control of the motor.
The speed control of such motor can be achieved usually by a change in the driving frequency, but the above-mentioned method, in which the driving frequency is always controlled by the resonance frequency, is unable to achieve a large change in the driving frequency, so that a large change in the revolution of the motor cannot be achieved.